This application is in the area of methods for the adjustment of pH in textile processes, recreational waters, and other aqueous liquids.
Fibers are processed in a number of ways before incorporation into textile products such as fabric and carpet. In a typical procedure in the case of nylon, nylon chip is first extruded and then converted into either continuous filament or staple fiber. The filament or staple fiber is then spun into yarn, and twisted and heat set as desired. The undyed, untreated yarn can be dyed and finished before or after fabrication into a final product.
The dying procedure can occur by batch or continuous operation. Again, in the case of nylon, in either operation, the dye bath typically includes an acid dye (i.e., a dye that adheres to the nylon under acidic conditions), a chelating agent, an acid dye leveler (an agent that promotes the even absorption of dye by the yarn), a wetting agent, and a pH adjuster (to insure acidic pH). The dye bath for continuous processing is typically maintained at a pH of between 3 and 6.5, and more typically, between 4 and 5. The dye bath for exhaust application is typically maintained at a pH of between 6 and 7, and more typically at approximately pH 6.5. The dyed yarn is then taken through a fixing step (usually moist heat), and rinsed.
The dyed yarn is finished by the application of desired finishing chemicals to the yarn, including stain blocking agents, fluorochemicals, fabric softeners, stabilizers, UV absorbers, optical brighteners, sewing assist agents, antistatic agents, waterproofing agents, durable resins, starches, and sizes. Some of these agents adhere more effectively when applied under acidic conditions. For example, common commercial stain blocking chemicals such as BASF Stain Protector and DuPont Stain resist chemicals are usually more effective when applied at a pH of between 1.9 and 2.5.
Fluorochemical polymeric finishes are usually applied at a pH of between 4 and 5. Coapplication of a stain blocking agent and a fluorochemical in a foam is often carried out at a pH of 3-5.
Yarns and fibers made from materials other than nylon can also be dyed or treated under acidic conditions. Wool and silk are typically acid dyed. Polyester is often disperse dyed with a solution that may have an acidic pH.
Traditional chemicals used for pH adjustment in textile processing include sulfamic acid, formic acid, sulfuric acid, phosphoric acid and combinations thereof. These pH adjusters can exhibit one or a combination of low efficiency (i.e., require large amounts of chemical for the desired effect), high cost, difficulty in handling, hazards in handling, corrosiveness, or high acidity of the resulting effluent stream.
One of the most commonly used pH adjustment systems in carpet processing is sulfamic acid ((HO)S(O).sub.2 NH.sub.2). Lower pHs can be attained with sulfamic acid than with comparable amounts of formic acid. Sulfuric and phosphoric acids will lower pH more efficiently than either sulfamic or formic acids. Corrosivity tests performed on carbon steel and stainless steel coupons show that all of these acids can be harmful to metal equipment.
The use of sulfamic acid increases the cost of textile processes because of the time and expense incurred to dissolve the powder, and the cost involved to repair and maintain corroded equipment. Further, as a significant amount of the acid used is carried into the effluent stream, the effluent must be neutralized to a significant extent with caustic prior to discharge to the water treatment facility, further adding to the cost of the textile process.
The object of the present invention is to provide a method for pH adjustment in textile processing that includes the utilization of a chemical that exhibits one or more of the properties of convenience, low corrosivity, efficiency of use, and minimal adverse impact on the environment.